The 7/7 bomb survivor's tricks of memory

At 8.50am on July 7 2005, Thomas, a 38-year-old computer scientist from Germany, was sitting on a tube at Edgware Road when, a few feet away, the suicide bomber Mohammad Sidique Khan blew himself up. The story of what happened to Thomas next was reported in this magazine for the first anniversary of the London bombings. He had remained conscious, and walked out of the wreckage with only minimal physical injuries. Yet for months afterwards he could remember almost nothing. No sight nor sound of the explosion, no image of mutilated passengers, no emotion. It was as if he hadn't been there.

At the time he first spoke to this magazine, Thomas's memory was still incomplete. He had been suffering a bewildering array of psychological symptoms, the worst of which was a paralysing concentration problem, which he described as an internal pressure that built up in his brain whenever he tried to set his mind to even the simplest task.

He had also been experiencing shocking flashbacks, in which he would catch the whiff of an appalling smell, or the sound of screaming, but nothing that formed a sequential memory. The strangest of his symptoms, however, was what happened if he laughed. When he found something funny or joyful, his laughter would be replaced, an instant later, by an overwhelming rush of horror.

This sudden switch of feelings turned out to be a kind of code for his lost memory. Four months after the London bombings, Thomas was diagnosed with post-traumatic stress disorder and referred to an NHS psychotrauma clinic for a programme of cognitive behaviour therapy. There, his therapist encouraged him to relive his experiences in order to "reprocess" them. As a computer scientist, Thomas appreciated cognitive explanations for how his "fight or flight" reflexes had short-circuited his memory systems, causing his mind to "dissociate". His disconnected memories were playing themselves out in repetitive loops. What he needed to find instead was a clear narrative sequence and a coherent emotional response.

The first clue came during one of his "relives", when he recalled that he had been reading a book by one of his favourite comic authors as he sat on the tube. Thomas realised that, at the moment of the explosion, he had been laughing.

This was a breakthrough connection. Thomas began to regain his concentration and a sense of reality. He was merging three separate pieces of the puzzle: his conscious memory, the shards of recollection from flashbacks, and the new recollections he got from therapy. But he still had no full visual image of the scene in the carriage after the blast. It was this last piece of the puzzle that he felt he needed to complete the therapy. Dreadful though it was, Thomas wanted to confront that picture.

He decided that the only way of achieving this was to see the 7/7 crime-scene photographs. It was a potentially risky request and, for several months, the police tried to put him off. But Thomas got the approval of the director of his psychotrauma unit and a date was set this summer.

When Thomas walked into the viewing session, however, it was to confront only disappointment. The pictures provided by the police were of the bare, twisted carriage, after it had been cleaned up. It was meaningless, except perhaps as a metaphor for his own amnesia: the distorted structures of memory were there, but emptied of their terrible contents.

The psychologist accompanying Thomas has since told him he can still try for a viewing of the real pictures. But Thomas recently started a new job and found that his concentration problems have mostly gone, so there is no longer any urgent clinical need. It seems that, among those closest to the 7/7 bombs, he was not only lucky to survive, but also fortunate in his ability to adapt. Now he has just the occasional flashback, or a moment when he'll laugh and find himself overcome by that old rush of horror.

Thomas has made peace with the fact that he will not put all the pieces back together. Yet he has also become acutely aware of what a remarkable piece of work is the brain. The effort to retrain his memory has produced some odd side-effects. Now when he plays a computer game during the day, he finds he can also play it at night, inside his own head. This is not a retinal replay of images, but an actual manipulation of the game scenario. It may be a minor consequence of trauma, but it says something powerful about the nature of memory. "Some part of my brain is picking up on those images and creating its own game," he says. "Although it sounds absurd, I'm reliving the game as if it were a reality."